1. Field of the Invention
The present invention concerns passive radar responders or answering equipment that allow to send back towards a radar, especially a Doppler radar, a much wider fraction of the signals emitted by said radar than that due to natural reflection on the most reflecting objects.
2. Description of the Prior Art
It is known to utilize as a passive reflector a rectangular trihedron of the "cube corner" type, or a Luneburg lens.
In a more complex manner, it is known to use a network of dipoles connected together to be in phase and connected to a short-circuit. The radar signal received is re-emitted at the pace of this manipulation in a direction determined by the antenna or aerial equivalent to the dipoles network. This network can be constituted for very short frequencies by a simple triplate circuit on which the dipoles are photoengraved. Thereby in band X with 8.times.8 dipoles disposed on a plate of about 30.times.30 cm.sup.2, a principal response lobe having an opening of 8.degree. is obtained. Such directivity is particularly useful when it is required to localize a point with discretion.
When the fixed echoes are eliminated, especially by using the Doppler effect, it is necessary to modulate the re-emission in order to simulate movement of the responder.